To expand the demand for bicycles to the elderly whose numbers are steadily increasing, various bicycles have been developed that can be ridden safely and comfortably by the elderly who are losing their physical strength including leg strength, balance sense, and alertness.
Such bicycles include three-wheeled cycles that have two rear wheels arranged side by side to support the load by three wheels including a front wheel. A three-wheeled cycle can stand upright without the rider controlling balance when not moving, and it has excellent stability when proceeding straight. When turning right or left, on the other hand, the rider cannot tilt the body of the bicycle supported by the three wheels and is instead forced to steeply lean his/her upper body toward the inside of the curve so as to balance with the centrifugal force. This approach, however, is hard especially for the elderly, possibly causing them to be swung outward by the centrifugal force, thereby getting off balance and hence turning over.
To avoid such a consequence, three-wheeled cycles having independent suspension wheels have been suggested as shown in FIG. 13, (see, for example, Patent Document 1). In such a three-wheeled cycle, two rear wheels “a, a” are each provided with a suspension and move vertically independently of each other. The left rear wheel “a” is chain-driven to allow the rider to control the steering of a front wheel “b”. The three-wheeled cycle allows the rider make a smooth turn by tilting the body of the cycle with the assistance of the individual suspensions.
The tilting of the body of the cycle, however, requires relatively soft suspensions. The soft suspensions work even when the cycle is not moving and may be felt as being wobbly by elderly riders who are losing their physical capabilities. Furthermore, the cushioning characteristics of the suspensions which work effectively when the bicycle is ridden on a rough road can be felt by elderly riders as unstable bouncing vibration.
When the rider steers to the right, the left rear wheel “a”, which is the drive wheel supports the right turn, thus allowing the rider to perform smooth cornering. When the rider steers to the left, on the other hand, the front wheel touches the road surface on the right side of the line extended from the drive wheel. As a result, the front wheel causes a force to act to prevent the left turn, thus failing to allow the rider to perform smooth cornering. The problem of not allowing the rider to perform smooth cornering in both right and left directions could be solved by providing a two-wheel drive mechanism having a differential gear. However, this would require a complex mechanism, having trouble with maintenance and increasing the production cost.
On the other hand, as shown in FIG. 14, bicycles with auxiliary wheels have been suggested (see, for example, Patent Document 2). The bicycle of FIG. 14 includes a spring means and a locking means. The spring means includes a U-shaped frame “f” and right and left arms “e, e”. The U-shaped frame “f” has a horizontal shaft “d” pivoted to a mainframe. The right and left arms “e, e” are bent backward from both ends of the horizontal shaft “d” and have auxiliary wheels “g” at their ends. The spring means presses the auxiliary wheels “g” downward, and the locking means prevents the rotation of the frame “f”. In this bicycle with the auxiliary wheels, the front and rear wheels are used during normal riding, and when the bicycle is stopped or moving slowly, the locking means locks the vertical movement of the auxiliary wheels, thereby avoiding the bicycle from falling over.
Patent Document 1: Japanese Patent Unexamined Publication No.
Patent Document 2: Japanese Patent Unexamined Publication No.